Study On The Design And Preparation Of C₇₀-based Stabilizer Based On Functionalized Modification And Its Stability On Nitrocellulose

The unstable nitrate ester group（O?NO₂）of nitrocellulose makes it easy to undergo slow or violent thermal decomposition in the daily storage and transportation process and under harsh conditions（high temperature or acidic）,resulting in nitrogen oxide free radicals and acidic autocatalytic products,triggering chain catalytic reactions,and finally lead to propellant performance failure.The accidental interaction between nitrocellulose components will also lead to the deterioration of propellant during long-term storage,which will have an adverse impact on the long-term storage safety of ammunition and the stability in extreme environment.The most effective method to enhance the stability of nitrocellulose is to improve the thermal decomposition characteristics of nitrocellulose with a stabilizer.Fullerene-based stabilizer is a novel stabilizer which has been studied in recent years and has the advantages of cleanliness and high efficiency.The traditional stabilizers have some disadvantages,such as poor thermal stability,saponification reaction is more possible to happen,and easy to produce toxic intermediates.Fullerene-based stabilizer has the advantages of high tolerance,good thermal stability and excellent scavenging ability of nitrogen oxide free radicals,it is considered as a potential alternative to existing propellant stabilizers.However,compared with C₆₀derivatives,the application of C₇₀derivatives with stronger electronegativity and free radical scavenging ability in stabilizers has not been studied.Twenty-one C₇₀-based stabilizers were designed and synthesized by the reaction of aromatic amine derivatives,N-arylglycine derivatives,malondiamide derivatives and phenol derivatives with C₇₀or C₇₀Cl₁₀.A new method of synthesizing C₇₀-based stabilizers by region selective synthesis of C₇₀Cl₁₀was proposed to solved the problem of excessive isomers in the functionalization of C₇₀.The relationship between the structure of C₇₀-based stabilizer and its stability,and the stabilization mechanism of C₇₀-based stabilizer were investigated based on its structural composition,electron-absorbing properties and nitrogen oxide radical scavenging ability.Then,the C₇₀-based stabilizers with the best stability were selected.The work includes the following five parts:（1）Seven arylamine C₇₀-based stabilizers and seven phenolic C₇₀-based stabilizers were prepared by nucleophilic substitution reaction between C₇₀Cl₁₀and arylamine derivatives or phenol derivatives.Four novel aryl C₇₀-pyrrolidine stabilizers were prepared by Prato reaction between C₇₀and N-arylglycine derivatives.Three arylmalonamide C₇₀-cyclopropane stabilizers were prepared by Bingel reaction between C₇₀and malondiamide derivatives.The structure of the products were characterized by spectroscopic analysis,and the advantages of C₇₀-based stabilizers with different structural are summarized.The structure of arylamine C₇₀-based stabilizer contains two groups that can enhance the stability of nitrocellulose.The yield of aryl C₇₀-pyrrolidine stabilizer synthesized by Prato reaction is the highest,and the synthesis conditions are mild,and it is easy to expand production.The arylmalonamide C₇₀-cyclopropane stabilizers are single mono-addition C₇₀derivatives,without any isomer,and the yield of synthesis reaction is high.A novel phenolic C₇₀-based stabilizers was synthesized for the first time using C₇₀Cl₁₀as a precursor,there are no other isomers,and C₇₀stabilizers with different number of functional groups can be obtained.（2）Methyl violet paper test,isothermal TG test and DTA were used to evaluate the thermal stability of C₇₀-based stabilizer to nitrocellulose.The influence of C₇₀-based stabilizer on the safe storage life of nitrocellulose was obtained according to Semenov’s equation,C₇₀-based stabilizer can increase the safety storage life of nitrocellulose.The influence of C₇₀-based stabilizer on the thermal decomposition parameters and the critical temperature of thermal explosion of nitrocellulose was obtained by Kissger’s method and numerical calculation method,the C₇₀-based stabilizer can increase the critical temperature of thermal explosion of nitrocellulose by 7.5℃.The interaction between C₇₀-based stabilizer and nitrocellulose was studied by DSC and ARC.The structure-activity relationship between the thermal stability and the structure of C₇₀-based stabilizer was studied.The reactivity of C₇₀-based stabilizer with the thermal decomposition products of nitrocellulose（for example,NO_x）was confirmed by ESR and FTIR,and the stabilization mechanism of C₇₀-based stabilizer was confirmed by the structural analysis of intermediates.Through the comprehensive comparison of C₇₀-based stabilizer of different functional groups as well as the different fullerenes influence on the thermal stability.The scavenging rate of C₇₀-based stabilizer with different functional groups on nitrogen oxide radical is in the order of arylamine cyclopropane,arylamine pyrrolidine,aniline,phenol.The order of discoloration time of methyl purple paper is aniline,aromatic amine cyclopropane,aromatic amine pyrrolidine,phenol.C₇₀-based stabilizer has stronger stability to nitrocellulose than C₆₀-based stabilizer with the same functional group.（3）Among the four types of C₇₀-based stabilizers,the arylamine C₇₀-based stabilizers showed the best thermal stability to nitrocellulose.However,the scavenging activity of arylamine C₇₀-based stabilizers to the autocatalytic decomposition products of nitrocellulose.The reasons for this difference were explored through a series of experiments.The structure of arylamine C₇₀-based stabilizer has both aniline functional groups with strong alkalinity and fullerene components with strong scavenging ability of nitrogen oxide free radicals.As both of them are functional groups with thermal stability function for nitrocellulose,the thermal stability of arylamine C₇₀-based stabilizer is significantly improved compared with ordinary stabilizers.The interaction energy between arylamine C₇₀-based stabilizer and nitrogen oxide free radical and the frontier orbital energy gap of arylamine C₇₀-based stabilizer were calculated.The basicity of arylamine C₇₀-based stabilizer was tested by perchloric acid non-aqueous titration.Finally,the change of thermal decomposition gas of nitrocellulose samples before and after doping with arylamine C₇₀-based stabilizer was measured by TGA-FTIR.（4）In order to reduce the production cost of fullerene-based stabilizer,the high efficiently and mass production of fullerene-based stabilizer were gradually developed,and the large-scale preparation method of aryl C₇₀-pyrrolidine stabilizer with the highest yield was studied.Through the comparative experiments of the properties of the fullerene-based stabilizer with different carbon atoms of fullerenes,and the characterization results of the non-fullerenyl stabilizer based on the principle of nitrogen oxide radical scavenging,it was confirmed that the main fullerene structure of the fullerene-based stabilizer has a stronger influence on its properties than other factors.Experiments show that C₇₀has better performance than C₆₀in scavenging nitrogen oxide radicals because of its stronger reductive and electron-absorbing properties.The addition of a small amount of aryl C₇₀-pyrrolidine stabilizer can significantly improve the thermal stability of aryl C₆₀-pyrrolidine stabilizer to nitrocellulose.Then,the fullerene soot was used as the precursor to explore the feasibility of low-cost preparation of fullerene-based stabilizer.Then,the mixed C₆₀/C₇₀fullerene-based stabilizer was prepared by one-pot method,and the thermal stability of C₆₀/C₇₀fullerene-based stabilizer on nitrocellulose was investigated.（5）Due to the unique structural of C₇₀,the selectivity of functional derivatization reaction of C₇₀is generally low,and it is easy to obtain multi-addition products or isomers.On account of the similar polarity of the multi-addition products,it is difficult to separate by common methods,which increases the difficulty in production and preparation.Based on the localization effect of secondary derivatization of C₇₀Cl₁₀,the regional selective synthesis of phenolic C₇₀-based stabilizer was carried out.A mono-addition arylmalonamide C₇₀-cyclopropane stabilizer was designed and synthesized based on highly selective cycloaddition reaction.The experimental results showed that the use of C₇₀Cl₁₀and phenol derivatives as precursors and the use of improved Bingel reaction can improve the selectivity of C₇₀-based stabilizer and the yield of the target product,therefore it can reduce the difficulty of the synthesis reaction of C₇₀-based stabilizer.It provides a new idea for large-scale preparation of fullerene-based stabilizer.